Traders are on edge Friday morning before a final decision is announced for the UK vote.

S&P 500 Index futures reversed an advance of as much as 0.7 per cent after results from Britain's European Union referendum in Newcastle-Upon-Tyne and Sunderland showed greater support for leaving the bloc than academics had forecast.

The debate over Britain's future dominated trading in June, with anxiety over the economic impacts of a Brexit, and the boost it could give to anti-establishment sentiment globally, stoking market volatility around the world.

Concern that the UK could secede has whipsawed stock markets this month, wiping more than US$1 trillion from global equity values last week alone. Bookmakers have been predicting a much lower chance of a "Leave" vote since the murder of pro-Europe UK lawmaker Jo Cox last week.